A widely used water heater for commercial and residential hot water production and storage is the electric resistance water heater. The electric resistance water heater typically includes a storage tank for retaining water and one or more electric resistance heating elements that heat the water in the storage tank.
Typical electric resistance water heaters are supplied with about 240V AC power. However, in certain circumstances a low voltage condition may occur where the water heater becomes connected to a lower voltage power source. For instance, the electric resistance water heater may be improperly miswired to a 120V AC source. Alternatively, a switching device used by the utility company or consumer to reduce peak load or to reduce power during high electric rate periods may reduce voltage from 240V AC to 120V AC. In addition, a brown-out may cause the voltage in a given area to sag to unacceptable levels for long periods of time.
The electric resistance heating elements used in electric resistance water heaters are intended for use at about 240V AC, but if a low voltage condition occurs, the electric resistance heating elements will still operate, just at reduced power. The electric resistance heating elements are not typically damaged by operating at lower voltages, such as at about 120V AC.
Recently, the heat pump water heater has been used as an alternative or in addition to electric resistance water heaters. A low voltage condition is more problematic for the heat pump water heater. The heat pump water heater includes various inductive loads, such as a motor-driven compressor and one or more evaporator fans, that are sensitive to voltage. In particular, as the voltage supply to the inductive load decreases, the current increases. For instance, if a compressor draws 3 A at 240V, it will draw 6 A at 120V. The higher current can lead to overheating of the motor windings, and potentially may cause the compressor or other inductive load to fail. Additionally, any electrical components in line with or sharing a common connection with the compressor or other inductive load may be damaged if the electrical components are not rated for the higher current caused by the low voltage condition. The resulting damage may require the heat pump water heater to be repaired or replaced, costing either the consumer or manufacturer a significant amount.
Thus, a need exists for a system and method that can detect a low voltage condition for a heat pump water heater. A system and method that can provide notification of the low voltage condition to an installer/user and protects the components of the heat pump water heater, such as the compressor, evaporator fans and other electrical components, from damage would be particularly useful.